Software Development Process Model - Part 1

Software Life Cycle Phases

• Requirements, analysis, and design phase.
• System design phase.
• Program design phase.
• Program implementation phase.
• Unit testing phase.
• Integration testing phase.
• System testing phase.
• System delivery.
• Maintenance.

The software process

• A structured set of activities required to develop a software system.
  • Specification
  • Design
  • Validation
  • Evolution
• A software process model is an abstract representation of a process. It presents a description of a process from some particular perspective.

Generic software process models

• The waterfall or linear sequential model
  • Separate and distinct phases of specification and development
• Prototype model
  • Requirements are not clear
• Rapid Application Development (RAD) model
  • High speed adaptation of linear sequential model

Waterfall model

Phases:

• Requirements analysis and definition
• System and software design
• Implementation and unit testing
• Integration and system testing
• Operation and maintenance
• The drawback of the waterfall model is the difficulty of accommodating change after the process is underway

Problems

• Inflexible partitioning of the project into distinct stages
• This makes it difficult to respond to changing customer requirements
• Therefore, this model is only appropriate when the requirements are well-understood

Prototyping Model

Prototyping Model:

• Requirements are not clear
• Iteration occurs as the prototype is tuned to satisfy the needs of the customer
• Prototype serves as a mechanism for identifying software requirements

Evolutionary development

Evolutionary development:

• Exploratory development
  • Objective is to work with customers and to evolve a final system from an initial outline specification. Should start with well-understood requirements
• Throw-away prototyping
  • Objective is to understand the system requirements. Should start with poorly understood requirements

Problems:

• Lack of process visibility
• Systems are often poorly structured
• Special skills (e.g. in languages for rapid prototyping) may be required

Applicability:

• For small or medium-size interactive systems
• For parts of large systems (e.g. the user interface)
• For short-lifetime systems

Process iteration

• System requirements ALWAYS evolve in the course of a project so process iteration where earlier stages are reworked is always part of the process for large systems.
• Iteration can be applied to any of the generic process models.
• Two (related) approaches
  • Incremental development
  • Spiral development